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Scientist: Changing Soil Management Could Improve Crops, Capture More Carbon

New Report: North America's Cropland Soils Have Lost Half Of Natural Carbon Content

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Healthy soil
Natural Resources Conservation Service Soil Health Campaign (CC-BY-2.0)

A recent report from the Intergovernmental Panel on Climate Change shows North America’s cropland soils have lost about half of their natural carbon.

The report goes on to say land degradation poses “one of the biggest and most urgent challenges” facing humanity.

Part of the solution could be in how we farm — and make them more productive and profitable in the process, said David Montgomery, a soil scientist at the University of Washington and author of “Growing a Revolution: Bringing Our Soil Back to Life.”

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But how did soil get to this state? Montgomery said if you look back at the history of agricultural societies around the world, there’s a legacy of land degradation.

“That really comes to the fore in places like Syria and Libya today where we don’t think of them as agricultural powerhouses, but if you go back to Roman times … there’s good tax records of high harvests of wheat off land where the soils have been so degraded now that they have real trouble supporting themselves,” he said.

There are two aspects contributing to land degradation, he said. The topsoil has been eroded, and the soil’s organic matter — which itself is half carbon — has been degraded.

Montgomery likens the microbes in the soil to that in the human gut. The bacteria and fungi in the soil helps plants acquire mineral nutrients and support their defensive systems.

Carbon is the “currency that drives the underground economy,” Montgomery said. The microbes in the soil break down the organic matter, moving mineral elements out of the soil and into plants.

“There’s symbiosis, sort of virtuous circles … where the life in the soil promotes the health and growth of plants, which then through their senescence and decay when they inevitably die as all things do, helps feed the organisms back in the soil and keeps the circle going,” he said.

Agricultural practices like tillage and heavy fertilizer use have degraded the soil’s fertility, and by default, the nutrition of the plants we eat, he said.

On top of that, heavy agricultural use has increased the amount of carbon released into the atmosphere, he said.

Plowing up fertile agricultural soil and accelerating the decay of organic matter speeds up the release of carbon back into the atmosphere, he said. Conventionally tilled soils erode at rates 100 times faster than they form, according to the report.

Montgomery pointed to a study out of the University of Washington in the early 1980s that looked at the amount of carbon added to the atmosphere since the industrial revolution.

“(It) found roughly a third of the carbon that had been added to the atmosphere up to about 1980 was from plowing up the Great Plains, plowing up Eastern Europe, from agricultural impacts that degraded soil fertility through the loss of soil organic matter,” he said.

While the news sounds grim, Montgomery said there’s potential to put some of that carbon back out of the atmosphere and into agricultural soils — changes that also could be more profitable for farmers because they harvest as much, but spend less to actually do it.

“That’s where I started to turn into a real optimist on this issue,” he said. “And it didn’t take that many years, just a couple in most cases, to start the trajectory of soil restoration back to the point where yields came back and recovered to where they were before the transition.”

Montgomery said there are three main agricultural practices that help the soil:

  1. Not tilling, which minimally disturbs the soil
  2. Using cover crops, whether it’s in between cash crops or having multiple crops growing at the same time
  3. Growing a diversity of plants, which helps support the microbial life in the soil

“With that combination of things … it feeds the life in the soil and allows farmers … to reduce their reliance on nitrogen fertilizers, to reduce their need for pesticides and to reduce the amount of tractor trips across the field,” he said.

And while the practices for implementing those changes on a small farm versus large industrial commodity farms are different, the ideas behind the practices are scalable, he said.

Estimates for how much carbon could actually be put back into the agricultural soils vary widely, ranging from about 10 percent of current fossil fuel emissions, up to more than 50 percent, Montgomery said.

“Reforming farming practices to rebuild the health and fertility of our land is not going to solve the atmospheric carbon problem, but it’s a really good down payment on doing so,” he said.

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